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| United States Patent |
5,298,826
|
|
Lee
, et al.
|
March 29, 1994
|
Rotor for rotary electrical machinery
Abstract
A rotor for rotary electrical machinery comprising a permanent-magnet
member made of a mixture having ferromagnetic material powder and a binder
resin for chief ingredients, and a shaft, in which a recess whose
projected contour on a plane orthogonally intersecting the axial line of
the permanent-magnet member is of a non-circular shape is provided at
least an end face of the permanent-magnet member, and a shaft is press-fit
into a metallic bush fitted to the recess, thereby ensuring high
coaxiality tolerance between the permanent-magnet member and the shaft,
easy assembly and low manufacturing cost.
| Inventors:
|
Lee; Takanobu (Matsudo, JP);
Matsushita; Ikuo (Matsudo, JP);
Take; Masao (Matsudo, JP);
Mifune; Masahiro (Matsudo, JP)
|
| Assignee:
|
Mabuchi Motor Co., Ltd. (Chiba, JP)
|
| Appl. No.:
|
979286 |
| Filed:
|
November 20, 1992 |
Foreign Application Priority Data
| Nov 21, 1991[JP] | 3-095299[U] |
| Current U.S. Class: |
310/156.09; 310/42; 310/43; 310/44 |
| Intern'l Class: |
H02K 021/12 |
| Field of Search: |
310/156,43,153,261,42,44,91
29/598
|
References Cited
U.S. Patent Documents
| 2680822 | Jun., 1954 | Brainard | 310/156.
|
| 2985779 | May., 1961 | Flaningam | 310/156.
|
| 3164735 | Jan., 1965 | Lichowsky | 310/156.
|
| 4674178 | Jun., 1987 | Patel | 29/598.
|
| 4748359 | May., 1988 | Yahara | 310/156.
|
| 4906882 | Mar., 1990 | Erndt | 310/156.
|
| Foreign Patent Documents |
| 0117567 | Sep., 1981 | JP | 310/156.
|
Primary Examiner: Skudy; R.
Attorney, Agent or Firm: McGlew and Tuttle
Claims
What is claimed is:
1. A rotor for rotary electrical machinery, comprising:
a permanent-magnet member of a cylindrical shape, said permanent-magnet
member being formed of magnetic material powder and a binder resin as
primary ingredients, said permanent-magnet member having a central axis
and having a recess with a projected contour on a plane of said
permanent-magnet member, said plane orthogonally intersecting said central
axis of said permanent-magnet member, said recess having an outer contour
which is non-circular in shape, said recess being provided on at least one
end face of said permanent-magnet member;
a metallic bush with a central hole passing therethrough, said metallic
bush having an outer contour corresponding to said outer contour of said
recess, said metallic bush being positioned within said recess with a
central point of said hole aligned with said central axis of said
permanent-magnet member; and
a shaft pressed fitted into said hole of said metallic bush.
2. A rotor for rotary electrical machinery as set forth in claim 1 wherein
said permanent-magnet member is formed into a substantially columnar
shape.
3. A rotor for rotary electrical machinery as set forth in claim 1 wherein
said permanent-magnet member is formed into a bottomed hollow cylindrical
shape, and a boss is provided including a plurality of radially provided
ribs formed integrally with said permanent-magnet member.
4. A rotor for rotary electrical machinery as set forth in claim 1 wherein
the projected contour of said recess and said metallic bush on a plane
orthogonally intersecting the axial line of said recess and said metallic
bush is a substantially quadrangular shape.
5. A rotor for rotary electrical machinery, comprising:
a permanent-magnet member of a cylindrical shape, said permanent-magnet
member being formed of magnetic material powder and a binder resin as
primary ingredients, said permanent-magnet member having a central axis
and having a recess with a projected contour on a plane of said
permanent-magnet member, said plane orthogonally intersecting said central
axis of said permanent-magnet member, said recess having an outer contour
which is non-circular in shape, said recess being provided on at least one
end face of said permanent-magnet member;
a metallic bush with a central hole passing therethrough, said metallic
bush having an outer contour corresponding to said outer contour of said
recess, said recess having a recess axial depth which substantially
corresponds to an axial depth of said metallic bush, said recess axially
depth being smaller than a length of said rotor, said metallic bush being
positioned within said recess with a central point of said hole aligned
with said central axis of said permanent-magnet member; and
a shaft pressed fitted into said hole of said metallic bush.
6. A rotor for rotary electrical machinery, comprising:
a permanent-magnet member of a cylindrical shape, said permanent-magnet
member being formed of thorough magnetic material powder and a binder
resin as a primary ingredients, said permanent-magnet member having a
central axis and having a recess on each end of said permanent-magnet
member with a projected contour on a plane of said permanent-magnet
member, said plane orthogonally intersecting said central axis of said
permanent-magnet member, said recess having an outer contour which is
non-circular in shape, said recess being provided on at least one end face
of said permanent-magnet member;
metallic bushes each with a central hole passing therethrough, each
metallic bush having an outer contour corresponding to said outer contour
of each said recess, each said recess having a recess axial depth which
substantially corresponds to an axial depth of a corresponding said
metallic bush, said recess axially depth being smaller than a length of
said rotor, each said metallic bush being positioned within a
corresponding said recess with a central point of said hole aligned with
said central axis of said permanent-magnet member; and
a shaft pressed fitted into said hole of said metallic bush.
7. A rotor for rotary electrical machinery as set forth in claim 6 wherein
said permanent-magnet member is formed into a bottomed hollow cylindrical
shape, and a boss is provided including a plurality of radially provided
ribs formed integrally with said permanent-magnet member, said boss
forming one end with one said recess.
Description
BACKGROUND OF THE INVENTION
This invention relates generally to a rotor for rotary electrical
machinery, including stepping motors, and more particularly to a rotor for
rotary electrical machinery using as a constituent element a so-called
bonded magnet made of a mixture having ferromagnetic material powder and a
binder resin for chief ingredients.
DESCRIPTION OF THE PRIOR ART
Conventional rotors for rotary electrical machinery using as a constituent
element a bonded magnet are usually of a construction shown in FIGS. 1 and
2. FIG. 1 is a perspective view, and FIG. 2 is a longitudinal sectional
view of a conventional type of rotor for rotary electrical machinery. In
FIGS. 1 and 2, numeral 1 indicates a permanent-magnet member formed of a
mixture of ferrite powder and a binding resin into a bottomed hollow
cylindrical shape. Numeral 2 indicates a boss to which a shaft 3 is
concentrically fixed. On the outer circumferential surface of the
permanent-magnet member 1 provided are a plurality of magnetic poles (not
shown) extending axially. By rotatably supporting the rotor in a stator on
which a wire is wound, an electric motor or generator is formed.
An efficient means for forming a rotor of the aforementioned construction
is molding the permanent-magnet member 1 and the shaft 3 integrally by
injection molding. That is, a shaft 3 is placed at a predetermined
location in a molding metal die, and a mixture of ferrite powder and a
binder resin is charged into the mold to integrally mold the shaft 3 with
the boss 2. In this process, it is generally practiced that a criss-cross
or axially parallel knurling pattern is provided in advance on the outer
periphery of the shaft 3 where the shaft 3 is integrally molded with the
boss 2, or so-called D-cutting (the cross-section of the shaft is machined
into a D shape) is performed, that is, a flat part 4 is provided on part
of the outer circumferential surface of the shaft 3, to ensure a firm
grip, or prevent the slipping, axial displacement or falling-off of the
shaft 3 due to the difference in thermal expansion coefficients of the
binder resin and the shaft 3 after molding.
By manufacturing a rotor in the aforementioned way, the unwanted slipping,
axial displacement or falling-off of the shaft 3 can be prevented, but the
conventional construction of rotors for rotary electrical machinery has
the following problems.
The shaft 3 and the permanent-magnet member 1 should preferably be
perfectly coaxial, and axial misalignment, if any, should be reduced to
the minimum. Too large an axial misalignment between the shaft 3 and the
permanent-magnet member 1 would make the gap between the rotor and the
stator uneven, leading to the deteriorated performance of the rotary
electrical machinery. In practice, however, it is extremely difficult to
completely eliminate the aforementioned axial misalignment, that is, to
obtain perfect coaxiality.
To mold the permanent-magnet member 1 and the shaft 3 integrally by
injection molding, as shown in FIGS. 1 and 2, the shaft 3 must be placed
in advance in a molding metal mold. In doing so, a certain gap is needed
between a shaft insert hole and the shaft 3 in the metal mold, and this
gap cannot be eliminated.
When the shaft 3 is placed in the molding metal mold, therefore, the shaft
3 can deviate to any one direction in the inside surface of the shaft
insert hole, or held in an inclined state with respect to the
predetermined axial line. Even when the shaft 3 is perfectly aligned with
the axial line, as a compound forming the permanent-magnet member 1 is
injected or poured into the molding metal mold, the shaft 3 can be
deviated or inclined from the predetermined axial line by the pressure of
the compound.
When the gap between the shaft insert hole and shaft 3 in the molding metal
mold is made extremely small to prevent the misalignment or inclination of
the shaft 3, it becomes troublesome to place the shaft 3 in the molding
metal mold, and extract moldings from the molding metal mold. This reduces
molding efficiency substantially.
Furthermore, if specifications of the shaft 3 is changed, the molding metal
mold must be replaced with a new one even when the permanent-magnet member
1 is the same in shape and in size. This results in increased mold
manufacturing cost, and requires additional work for mold replacement.
This lowers the ratio of the molding of the rotor proper to the entire
molding work, including tooling, leading to increased cost. The
aforementioned machining, such as knurling, is needed to prevent the shaft
3 from slipping, displacement and falling, increasing machining cost. In
addition, the need for using soft materials to make this machining easy
inevitably reduces mechanical strength.
SUMMARY OF THE INVENTION
This invention is intended to overcome the problems inherent to the prior
art described above. It is an object of this invention to provide a rotor
for rotary electrical machinery that can accomplish high coaxiality
between the permanentmagnet member and the shaft, good workability and low
manufacturing cost.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1 and 2 are a perspective view and a longitudinal sectional view
illustrating the essential part of a conventional rotor for rotary
electrical machinery.
FIG. 3 is a perspective view illustrating the essential part of an
embodiment of this invention.
FIG. 4 is an exploded perspective view showing components of an embodiment
of this invention shown in FIG. 3.
FIGS. 5 through 7 are a longitudinal sectional view, left-side view and
right-side view of another embodiment of this invention.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 3 is a perspective view illustrating the essential part of an
embodiment of this invention, and FIG. 4 is an exploded perspective view
showing components of an embodiment of this invention shown in FIG. 3.
Like parts are indicated by like numerals shown in FIGS. 1 and 2. In FIGS.
3 and 4, numeral 5 refers to recesses provided coaxially on both end faces
of the permanent-magnet member 1. The recesses 5 are formed into a square
shape in the projected contour on a plane orthogonally intersecting the
axial line of the permanent-magnet member 1. Numeral 6 refers to a
through-hole formed coaxially with the permanent-magnet member 1 into an
inside diameter slightly larger than the outside diameter of the shaft 3,
or an inside diameter having a certain press-fit allowance. The
permanent-magnet member 1 of this type can be formed by injection molding,
for example.
Numeral 7 refers to a metallic bush made of sheet metal, for example, and
formed by pressing or punching means into a square shape in outside
contour, and the size of the metallic bush 7 corresponds to the recess 5,
with a hole 8 coaxially provided at the center thereof. The inside
diameter of the hole 8 is made slightly smaller than the outside diameter
of the shaft 3 so that resistance to falling of the shaft 3, when
press-fitted, as will be described later, can be maintained at over 20
kgf, for example. The shaft 3 is formed into a substantially equal outside
diameter along the overall length.
With the aforementioned construction, the rotor is assembled by
press-fitting the metallic bushes 7 into the recesses 5 on both end faces
of the permanent-magnet member 1, then press-fitting the shaft 3 into the
hole 8. Since the outside contour of the metallic bushes 7 is formed in
such a fashion as to correspond to that of the recess 5, coaxiality
between the permanent-magnet member 1 and the hole 8 can be maintained by
press-fitting the shaft 3 into the recess 5. As the shaft 3 and the hole 8
are fixedly fitted to each other by press-fitting, the slipping, axial
misalignment or falling of the shaft 3 can be prevented.
FIG. 5 is a longitudinal sectional view illustrating the essential part of
another embodiment of this invention, FIG. 6 is a left-side view of the
same, and FIG. 7 a right-side view of the same. Like parts are indicated
by like reference numerals shown in FIGS. 1, 2, 3 and 4. In FIGS. 5
through 7, the permanent-magnet member 1 is formed into a bottomed hollow
cylindrical shape and has ribs 9 therein. The construction of this
embodiment is the same as the embodiment shown in FIGS. 3 and 4, except
that the recesses 5 are provided on the bottom end face of the
permanent-magnet member 1 and on the end face of the boss 2. Consequently,
the method of assembly, the maintenance of coaxiality between the
permanent-magnet member 1 and the shaft 3, and prevention of the slipping,
axial misalignment or falling of the shaft 3 are also the same as in the
embodiment shown in FIGS. 3 and 4.
In this embodiment, description has been made about the use of ferrite
powder as the most commonly used materials for the permanent-magnet
material. Needless to say, known ferromagnetic materials other than
ferrite, such as Sm-Co or Nd-Fe-B and other rare-earth magnet materials
having excellent magnetic properties may be used as ferromagnetic material
powder. Furthermore, known resin materials, such as nylon, may be used as
the binder resin. Injection molding has been described in this embodiment
as the means for molding so-called bonded magnets, but other molding means
may be used. This invention may be applied to anisotropic bonded magnets
manufactured in a magnetic field. The metallic bush and the recess may be
provided at least an end face of the permanent-magnet member, and the
shape of them may not be limited to a square shape, but rectangular,
triangular, polygonal, elliptical and other geometric shapes other than a
non-circular shape can be used so long as the slipping of the shaft can be
prevented.
This invention having the aforementioned construction and operation can
accomplish the following effects.
(1) Since the permanent-magnet member can be molded separately, molding
efficiency can be increased and the coaxiality of the permanent-magnet
member with respect to the shaft can be improved substantially.
(2) Molding metal molds need not be changed even for different lengths of
the shaft. This can substantially improve productivity in the short
production run system in which a small quantity of a wide variety of
products are manufactured.
(3) The shaft can be formed into an equal diameter, and the knurling or
D-cutting of the shaft as practiced in the prior art is eliminated. This
leads to reduced machining cost.
(4) Since no additional machining of the shaft is needed, the material of
the shaft can be selected freely, and even high-strength materials can be
used.
(5) The shaft can be fixedly fitted to the permanent-magnet material by
press-fitting the shaft into the non-circular metallic bush. The slipping,
axial displacement or falling of the shaft can be prevented.
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